I've set up Google Voice -> US SIP -> UK SIP -> 3 Mobile. This gives me a US number to give out to Americans (who don't want to dial my UK number) that they can text/call. I can then make calls when on Wifi or using a Phonecard app which automatically dials my UK SIP and forwards the call via the US SIP provider. I don't have to switch SIMs or give up my UK number.
This works well for me (since I travel between the US/UK often)
This works well for me (since I travel between the US/UK often)